[FIX] l10n_ae: fix vat amount computation

Current behavior:
If you make a sale in the PoS without invoicing it, the vat amount in
the tax report was no correctly computed.

Steps to reproduce:
- Install l10n_ae
- Create a payment method and a PoS with this payment method
- Create a product with a price of 100 AED and the tax of 5% (Dubai)
- Make 2 pos orders with this product, one with invoicing and one
  without
- To see the VAT Amount we need to add it with studio, go in accounting
  -> journal items -> studio -> existing field -> "vat amount"
- Go in the accounting app and go for the Tax Report, change the date
  range to the financial year. Now click on "Dubai" in the "Standard
  Rated Supplies (Base)" section. And click on "Audit"
- You will see that the VAT amount of the order is 0 when it should be 5

opw-3293589

closes odoo/odoo#127796

X-original-commit: e580636b3f5b4404a843fd5afb6abd426787b6bf
Signed-off-by: Joseph Caburnay (jcb) <jcb@odoo.com>
Signed-off-by: Robin Engels (roen) <roen@odoo.com>